Polyester polyols produced from dicarboxylic acid anhydrides, polyols and polyepoxides are known. For example, in U.S. Pat. No.4,403,093, such polyester polyols are produced by first reacting a 1,2-dicarboxylic acid anhydride with a polyol under conditions sufficient to form a half-ester which is then reacted with a polyepoxide. The resultant polyester oligomers are described as being useful as resinous binders in high solid containing compositions.
Polyester polyols produced from aromatic acids and polyoxyethylene glycols are known and are described as being useful in the production of rigid polyurethane foams (see, e.g., U.S. Pat. No.4,039,487 and German Auslegeschrift 1,155,908).
In the known polyurethane/urea reaction injection molding (RIM) process, a wide variety of different polyols have been suggested (see e.g., U.S. Pat. Nos. 3,726,952, 4,218,543, 4,288,564, 4,442,235, 4,519,965, 4,581,396, 4,764,540, and 4,789,688; and British Patent 1,534,258. Similarly, polyester polyols of various types have been suggested for use in the RIM process (see, e.g., U.S. Pat. Nos. 4,065,410, 4,481,309, 4,590,219 and 4,595,705).
U.S. Pat. No.4,065,410 discloses a RIM process requiring a three-component polyol system that includes a polyhydroxyl compound having a molecular weight greater than about 1800 and a chain extender mixture consisting of ethylene glycol and at least one other polyol having a molecular weight below about 1800. The reference indicates that the higher molecular weight polyhydroxyl compounds can include polyester polyols derived from polyhydric alcohols and polycarboxylic acid but does not describe the use of polyester polyols as the lower molecular weight polyol component of the chain extender mixture. In contrast, the aromatic polyester polyols of the present invention, despite having molecular weights no greater than 1500, have been found to provide surprisingly advantageous processing advantages when compared to aromatic polyester polyols of the type described in the reference.
U.S. Pat. No.4,590,219 discloses a process using ester-terminated polyether polyols, polyester polyols formed from a mixture of at least three polyols, or a mixture thereof. The ester-terminated polyether polyols are formed by reaction of polyether polyols with lactones and are unlike the polyester polyols of the present invention. The polyester polyols are prepared by condensation of preferably aliphatic dicarboxylic acids and a mixture of at least three polyols.
U.S. Pat. No.4,595,705 discloses a RIM process using mixtures of conventional polyols and low molecular weight aromatic polyester polyols having molecular weights no greater than 700. In contrast, the polyester polyols used in the present invention are always aromatic and have molecular weights of about 840 to 1500 and provide excellent processing properties, even in the absence of the conventional polyols described in the reference.